ES DIY Motor Challenge

[vanilla ice]

I don't get the fascination with torque, power is what we need.. Use that as your metric. Power is usable torque.

[Miles]

It's not a fascination with torque, it's the importance of torque density..... For the purpose of comparing a broad range of motor sizes, torque density is a pretty good measure. It does slowly increase with motor size, hence the 3 kg limit.

Does anyone else disagree with the parameters I've chosen?

[John in CR]

Yes, no weight limit, since torque density already covers mass. That opens it up to more variety, and leaves the decisions of power and weight up to the builder to consider the legalities in their jurisdiction. Also someone may want to DIY an axial flux hub motor, which will add weight just because it's going in a wheel.

John

[Miles]

John,

Like I said, larger motors do have an advantage. That's the reason for the 3kg limit. This is the non-hub motor forum

0.5kg to 3kg should be the range that most people want to work within?

[John in CR]

Rules, rules, rules...some of us don't like rules, and now a better than currently available hub motor can't play. I guess brushed motors are out too...What about 6 phases?...Voltage limits?...Does it have to be a certain color?

[mwkeefer]

John,

Just put the nylon gears back in, seperate the mag ring and drill the thing from the backside divits to reduce weight and finally drill the living crap out of your covers - I'm talking 1" or bigger diameter holes... and run it without any lube - try teflon power like you use for a bowling ball - be sure you have it mounted to a suspension fork and if you still need to loose some weight... well start unwinding every third phase or so... maybe a cromo axle or somthing stronger and lighter than the factory axle? Magnesium is awful light (and as strong as aluminum if cast properly) - Half Kidding

Um... fellas maybe title should include the word Electric, ie: "ES DIY Electric Motor Challenge" - or can I submit the my wenkle design rotary gas powered ebike/lev hub motor? - (Kidding and no, I won't do the photoshop)

I've only ever built 1 electric motor from scratch, I was 6 years old and it was nails, magnets and that Green xmas wire for windings - add 9v battery and a flick of the finger (can you say pedalec) and I was hooked for life.

-Mike

[recumpence]

I've only ever built 1 electric motor from scratch, I was 6 years old and it was nails, magnets and that Green xmas wire for windings - add 9v battery and a flick of the finger (can you say pedalec) and I was hooked for life.

-Mike

Oh, Man, I built one of those myself. I think I was 7 or 8, though. So, you got the jump on me!

Matt

[mwkeefer]

Matt, I hate to admit but I think this is turtle vs hare {I'm the hare, roadkill on I95} and we all know who won that race {hint: its not the guy with the green bailing wire direct drive motor running 9v} - Mike

[spinningmagnets]

Axel from Sweden sent me a rough draft of a manual (with lots of pics) to build a home-made 6" axial-flux 500W@36V motor and DIY opto-controller. It is for an RC plane, and it is only one-phase. He has recieved a lot of interest and is putting together a tutorial for a much larger 3-phase axial (should be available in 6 months), which he plans to sell the PDF for a modest price.

I plan on scaling down his 3-phase motor to a 1,000W@48V to power a DIY longtail bike. I just picked up a used Sturmey-Archer 3-speed hub I hope to use as a jackshaft/transmission, and I may go ahead and build the bike with a temporary TNC motor as it will be months before I will even start building an "Axel"-motor. At this rate, it might take 9 months, wish me luck...

[amberwolf]

Um... fellas maybe title should include the word Electric, ie: "ES DIY Electric Motor Challenge" - or can I submit the my wenkle design rotary gas powered ebike/lev hub motor? - (Kidding and no, I won't do the photoshop)

Something like this, but using Wankel?
http://en.wikipedia.org/wiki/File:Felix_Millet.jpg

[Thud]

While i am thinking of it I have several versions of my axial designs draw in cad, I can easily convert them to a pdf & they are free for the taking. I just need to add some dimensions to the models.
if any one is interested.

[liveforphysics]

This is interesting reading on this topic:

http://www.grc.nasa.gov/WWW/RT/2006/RX/ ... ebert.html

It kinda shows why the decision to make this about specific torque makes for a more EV applicable challenge than specific power. If we make it about specific power, it's going to come down to doing 1 turn windings all in parallel with 4 magnet rotors, ceramic bearings, and long thin motors pushing things into the 50-100,000rpm area. It would be very cool purely from an engineering perspective, but it's going to need a real PITA reduction setup to make it useful for an EV. It's also going to get expensive very quickly with the need for super-materials to withstand extreme RPM G'forces.

Torque/weight allows a normal guy working with model aircraft plywood, a hand router, and a small budget can win if he comes up with the most clever design, rather than having it be about who can afford the best ceramic bearing technology and magnets lashed onto a rotor with kevlar thread and a 1/4" air gap to jump the KV into the 5,000RPM/V range.

Who ever can make the most torquey design by weight could also be the most powerful by weight with enough voltage and adquate rotor material strength.

[Miles]

Who ever can make the most torquey design by weight could also be the most powerful by weight with enough voltage and adquate rotor material strength.

Thanks Luke. I couldn't have put it better.

[liveforphysics]

Anyone thought about how we are going to do the testing?

We gotta have them all tested on the same piece of equipment by somebody we all trust. That means I'm out, because I freely admit that I cheat to win anything I'm entered in, and I will be entering this.

I would trust Miles to fairly and accurately test torque on the motors, but he is in England, which would be kinda strange for shipping bizzare things both ways. Also, I would love to have you enter Miles! It could be your first motor build

All the automotive dyno-cells I've got access to don't start to read torque until 50ft-lbs.

Any ideas about who can do the testing? I know BigMoose is as honest and capable as any on earth, but he is up to his eyeballs in NASA projects right now

I've spent 2hours tonight just shopping magnets for this... lol The magnet is the part I can't make myself, you you essentially need to pick a magnet layout first, then design the motor around it. It actually feels a lot like building a race engine. So many magnet choices, and all of them comprimises in some way or another.

[Miles]

How about we design, and build collectively, a robust dyno test set-up? This could be shipped to each person when they are ready to test their masterpiece... Is this a viable alternative to having one person do the testing?

What's needed in the test? Proof of torque level sustained for 30 minutes? Proof of weight.

[fechter]

Since the objective is to make a motor that can push a bike, I think it's fair to include the overall gearing to the wheels in the efficiency measurement.

One measurement would be the watt-hours per km at a specific speed. Anyone with a CycleAnalyst or similar device can make this measurement. This is really what we're after in the end.

Here's an interesting motor design: http://www.evilmadscientist.com/article.php/HomopolarMotor
I made one of these and it always got going so fast the rotor flew off. Now how do you make a brushless version of it?

I once tried taking an old car alternator and shorted the field winding on the rotor and fed the stator with 3 phase from my scooter controller. With the field coil shorted, the thing acts like an induction motor. I don't think I had the drive optimized and it was running open loop, but the thing got spinning really, really fast. So fast that I was worried about it flying apart. Had no torque however.

Alternator test setup.jpg (65.66 KiB) Viewed 941 times

Here's an interesting coreless axial motor. The magnet is a solid ring that's magnetized with poles in a Hallbach array. There is non-moving back iron behind the coils, so I don't think it is very efficient. You can see the hall sensors in the middle of the upper left coils.

Axial ironless axial motora.jpg (37.83 KiB) Viewed 974 times

Here's another good motor, the AstroFlight AF3210. This has overlapping windings similar to a Crystalyte hub motor. I wonder how they keep the rotor from flying apart at high rpm?

AstroFlight_AF3210-12T-02.jpg

(151.48 KiB) Downloaded 484 times

One of my earlier motor projects was my Zappy motor. After burning it up twice, I replaced the wimpy ceramic magnets with some really strong Neodynium ones that just happen to fit the curvature of the motor housing. This allowed me to rewind the armature with about half the turns of much heavier wire. The result had at least 5x the power of the original motor.

A-0059.jpg (68.05 KiB) Viewed 942 times

[Thud]

Looks like we have a 3rd, Welcome LFP!

Miles, Are you building a motor?

Roll call: every one/anyone who wants to build a motor chime in. what do you need?

I did finish that eddy brake, But I kinda over tested it- dynoing my lathe. (melted the glue holding the rotor assembly togeter)lathe-1 dyno-0.

I plan to build a reasonably sized unit for testing my motors, so that is an option.

Let the debate begin on testing parameters

[Miles]

I'm not sure we need to test efficiency directly for the challenge?

If you achieve the highest sustainable specific torque, that will be largely due to having the best efficiency, I would have thought?

It would certainly be good to have the data. I'm not sure efficiency needs to be a challenge parameter, though..?

[Miles]

Here's an interesting motor design: http://www.evilmadscientist.com/article.php/HomopolarMotor

Thanks for that. I love it

[Malcolm]

I might just stand a chance of competing if you change the challenge parameter to "number of motors built in five minutes".

I just built two of the homopolar motors. Brilliant

[etard]

Why can't we test it the same way the rc guys do and just set a limit on rpm/volt? A simple test stand with a digital weight scale to measure the pull of the prop for 30 minutes. I also am throwing the hat in the ring simply because I want to learn more about the science and tolerances of these motors. I just want to keep this fun, we font need to get hung up on rules and cheating and loopholes, rather we should be a community that shares and gives good ribbings.

We should also standardize the controller to be used for testing. We also need somebody to come forward who knows what they are doing to set out the rules in stone and volunteer to test and devise the rig for testing. Next all entrants chip in for the test rig and send the motor along with payment for return shipping. I think we need 10 entrants to make this interesting and then set a date in the not too distant future.

John,
I think the weight limit is fair, it's just that you are trying to build a train motor and the rest of us would like to build a BICYCLE motor. Maybe we can set a secondary test that will award the entrant with most power so that larger motors will win this shootout?

[Miles]

Why can't we test it the same way the rc guys do and just set a limit on rpm/volt?

Hi etard,

What's that to do with?

[etard]

Miles,
Nevermind, that's gonna be a measurement of thrust and not really comparable to our purposes. I was mostly pointing out a method already in use.

I might just have a go at rebuilding my Hacker motor and submitting that. I wanted to delta/wye it anyway. Is that permissable? Or what if I overbuilt it with better and bigger bearings, and a stouter shaft with better magnets, maybe add sensors do you guys have any objections to this approach?

[John in CR]

John,
I think the weight limit is fair, it's just that you are trying to build a train motor and the rest of us would like to build a BICYCLE motor. Maybe we can set a secondary test that will award the entrant with most power so that larger motors will win this shootout?

Etard,
No, not a train motor...motorcycle motor maybe. My advantage is the lack of e-bike rules here in Costa Rica, so all I need is pedals and it's legally a bike as long as it doesn't have a piston displacement > 49cc. I have no interest in electric motors with pistons.

Miles,
Won't a larger diameter result in greater torque for a given weight more than higher efficiency would? If it's not as efficient then it just needs better cooling.

[Miles]

Miles,
Won't a larger diameter result in greater torque for a given weight more than higher efficiency would? If it's not as efficient then it just needs better cooling.

The dyno and the scales will be the judge of that..........

Certainly, you'll get higher sustainable torque level through a better heat dissipation rate.